1. Field of the Invention
The present invention relates to improvement of circuit configuration technique of an integration-discharge circuit appropriate for the case of converting frequency of the signal into voltage in order to demodulate voice band FSK (Frequency Shift Keying) signal.
2. Description of the Related Art
Generally, an integration-discharge circuit is configured so as to execute a series of operation. In the integration-discharge circuit, integration is made to execute on input signals during specific times, followed by holding to be taken the integrated voltage directly or followed by holding to be taken the integrated voltage after sampling, and executing a series of operation for discharging the integrated voltage for the sake of next integration operation. For that reason, conventional integration-discharge circuit required the center integration circuit and the peripheral some gate circuits and further the control signal generation circuit for controlling these gate circuits with appropriate timing. Furthermore, in many cases, generally, analog switch is used for ON/OFF of input signal for the integration circuit, gate for ON/OFF of sampling and/or holding of integrated voltage, gate for discharge of integrated voltage and so forth. Dedicated IC for the hold is used in the hold circuit.
Integration-discharge operation based on the conventional circuit configuration requires complicated circuit configuration and high cost. The conventional integration-discharge circuit includes the integration circuit, a plurality of gate circuits and the control signal generation circuit. The integration circuit, a plurality of gate circuit and the control signal generation circuit are combined to realize the integration-discharge operation depending on coordinate operation of these circuits. Accordingly, the present inventor investigates to achieve this problem. And he has found that an integration-discharge circuit with simple circuit configuration is capable of being realized while utilizing FSK signal itself as the control signal. When the FSK signal is demodulated, polarity of the signal voltage of the FSK signal has a phenomenon of sign inversion in every half cycle of AC signal of the FSK.
In view of the foregoing, it is an object of the present invention is to provide a FSK signal demodulation integration-discharge circuit.
According to a first aspect of the present invention, a FSK signal demodulating integration-discharge circuit comprising converting means for converting FSK signal into rectangular-wave signal, an integrating capacitor which charges the rectangular-wave signal therein in such a way that charging is made to execute corresponding to a portion of positive voltage or negative voltage of said rectangular-wave signal according to ON/OFF of a first transistor that is turned ON/OFF due to said rectangular-wave signal, while which integrating capacitor discharges the rectangular-wave signal therefrom in such a way that discharging is made to execute corresponding to a portion of positive voltage or negative voltage of said rectangular-wave signal according to ON/OFF of the first transistor that is turned ON/OFF due to said rectangular-wave signal, a holding capacitor which charges the charged voltage of the integrating capacitor therein in such a way that charging is made to execute corresponding to a portion of positive voltage or negative voltage of said rectangular-wave signal according to ON/OFF of a second transistor that is turned ON/OFF due to the rectangular-wave signal, while which holding capacitor discharges the charged voltage of said integrating capacitor therefrom in such a way that discharging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of the second transistor that is turned ON/OFF due to the rectangular-wave signal, and taking out means for taking out a voltage which is subjected to holding by the holding capacitor.
According to a second aspect of the present invention, in the first aspect, a FSK signal demodulating integration-discharge circuit, wherein the taking out means takes out the voltage which is subjected to holding through a high input impedance circuit.
According to a third aspect of the present invention, a FSK signal demodulating integration-discharge circuit comprising converting means for converting FSK signal into rectangular-wave signal, a first integrating capacitor which charges the rectangular-wave signal therein in such a way that charging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of a first transistor that is turned ON/OFF due to the rectangular-wave signal, while which first integrating capacitor discharges the rectangular-wave signal therefrom in such a way that discharging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of the first transistor that is turned ON/OFF due to the rectangular-wave signal, a first holding capacitor which charges the charged voltage of the integrating capacitor therein in such a way that charging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of a second transistor that is turned ON/OFF due to the rectangular-wave signal, while which first holding capacitor discharges the charged voltage of the integrating capacitor therefrom in such a way that discharging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of the second transistor that is turned ON/OFF due to the rectangular-wave signal, an inverting means for outputting an inversion rectangular-wave signal while inverting a phase of the rectangular-wave signal, a second integrating capacitor which charges the rectangular-wave signal therein in such a way that charging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of a third transistor that is turned ON/OFF due to the rectangular-wave signal, while which second integrating capacitor discharges the rectangular-wave signal therefrom in such a way that discharging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of the third transistor that is turned ON/OFF due to the rectangular-wave signal, a second holding capacitor which charges the charged voltage of the integrating capacitor therein in such a way that charging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of a fourth transistor that is turned ON/OFF due to the rectangular-wave signal, while which second holding capacitor discharges the charged voltage of the integrating capacitor therefrom in such a way that discharging is made to execute corresponding to a portion of positive voltage or negative voltage of the rectangular-wave signal according to ON/OFF of the fourth transistor that is turned ON/OFF due to the rectangular-wave signal, and taking out means for taking out a voltage which is subjected to holding by the first or the second holding capacitor.
According to a fourth aspect of the present invention, in the third aspect, a FSK signal demodulating integration-discharge circuit, wherein the taking out means takes out the voltage which is subjected to holding through a high input impedance circuit.
The various features of novelty which characterize the invention are pointed out with particularly in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.